1. Field of the Invention
The invention relates to the field of magnetic data storage and, more particularly, to an apparatus for confirming the integrity of data stored on tape cartridges or other physical volumes by providing a mechanism for detecting a bulk erasure or other corruption of the magnetic media.
2. Related Art
Magnetic tapes can be used to store a variety of information, such as audio or visual signals and binary data readable by a computer system. The widespread use of magnetic tapes is due, in part, to the ease with which data on tape may be rewritten. Moreover, a magnetic tape can be completely erased and then reused.
Two basic methods have been used to erase magnetic tape. The first method involves placing the tape into a tape drive which will unwind the tape from the supply reel and run it across a degaussing head. This technique takes a considerable length of time and can be especially time consuming with very large reels of tape.
In a second traditional method, the tape is placed into a bulk tape eraser mechanism. The bulk tape eraser mechanism uses a relatively high-intensity magnetic field to degauss the entire reel of tape. This is known as a bulk erasure.
In addition, data stored on a tape may be damaged by intentional or unintentional exposure to a magnetic field of sufficient intensity to alter the state of the data recorded on the magnetic medium. Such a field may be generated by an unshielded permanent magnet or other source of a static or alternating magnetic field.
As the computer and data processing industries store more and more different types of data on magnetic tape cartridges and other magnetic media (e.g., magnetic disks), it is becoming increasingly important to be able to assure or confirm the integrity of the data stored on the media. For example, it may be desirable in certain record archival situation to prevent data on a magnetic tape from being modified. Storage Technology Corporation of Louisville, Colo., has developed a system which allows a magnetic tape recording system to emulate a write-once capability. This system is disclosed in commonly owned U.S. patent application Nos. 07/791,489, filed Nov. 12, 1991, entitled "Method and Apparatus for Administering Data on Magnetic Tape Media," and 07/896,106, filed Jun. 9, 1992, entitled "Method and Apparatus for Managing Data on Rewritable Media to Define Read/Write Operational Status," both of which are incorporated herein by reference.
The system disclosed in these copending patent applications prevents modifications from being made to data stored on a magnetic tape. However, another problem remains in assuring/confirming the integrity of data stored on magnetic tapes. A tape may be bulk erased, and a user may not be able to discern a tape which has been bulk erased from a tape which never had data stored on it. In addition, data stored on the tape may be corrupted by exposure to a magnetic field of insufficient intensity to completely erase the tape. The present invention is directed toward providing a corruption/bulk erasure detector for use with magnetic tapes or other magnetic media volumes.